JP2009234028A - Optical film, manufacturing method for it, polarizer using optical film and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture an optical film used for a polarizer protective film of a liquid crystal display (LCD), etc., hardly causing deterioration of quality such as creases and scar due to dispersion in separation performance, and dispersion in retardation to thereby meet requirements for widening and quality improvement of a polarizer protective film or the like. <P>SOLUTION: A method for manufacturing the optical film using a solution-casting film-making process includes a casting zone A, a web drawing zone B and a web drying zone C, wherein after the casting zone A, one of the drawing zone B and the drying zone C is disposed, and the other is disposed after that. An ultraviolet irradiation device and/or normal pressure plasma device is installed in one zone to zone transition part out of zone to zone transition parts of the zones different in atmospheric temperature, or all of zone to zone transition parts, thereby performing high energy treatment to the web transferred through the zone to zone transition part with ultraviolet irradiation and/or normal pressure plasma irradiation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides an optical film that can be used for various functional films such as a protective film for a polarizing plate used in a liquid crystal display (LCD), a retardation film, a viewing angle widening film, and an antireflection film used in a plasma display. The present invention relates to a method, an optical film, a polarizing plate, and a display device.

  In recent years, liquid crystal display devices have come to be used in televisions and large monitors due to improvements in image quality and high definition technology. In particular, these liquid crystal display devices are costly due to their large size and efficient production. The demand for down and the like has become stronger in materials for liquid crystal display devices, and a wider optical film is required.

  In recent years, the demand for optical films has been increasing rapidly in response to the rapid growth of liquid crystal TVs, and there is a strong demand for improved productivity. In order to cope with an increase in the screen size of a liquid crystal TV, it is necessary to make a wide film that is wider than a conventional film. In addition, an increase in production speed is also necessary, but with the conventional drying zone length, the web drying time is shortened and the film is not sufficiently dried, leaving a trace amount of solvent. It is necessary to stretch or increase the drying temperature. The former is not practical because the production process needs to be stopped for a long period of time and a large-scale remodeling work is required, and the latter method is generally used. However, the method of increasing the drying temperature also increases the evaporation rate of additives contained in the web, such as plasticizers, UV absorbers, retardation control agents, peelability improvers, etc. There was a problem that the concentration increased and condensation was likely to occur.

  For example, if condensation such as additives occurs in the drying zone and accumulates on the upper wall or the like of the drying zone, it drips down and soils the web and the transport roll. In the film portion to which the dirt is attached, a strong pattern can be seen at a glance and cannot be used as a product. In addition, even very slight condensation that cannot be seen by visual observation makes the web surface slippery at high temperatures, which means that the web width between the transport rolls, which is normally suppressed by the friction between the transport rolls and the web, can be reduced. When winding a web that has been shrunk in the direction or has come out of the drying process and cooled to near room temperature, the slipping property of the part to which the condensation has adhered is reduced, and it acts as if it is caught during winding. In addition, partial deformation of the film is likely to occur, and even when the wound film is stored, the films tend to stick to each other. In addition, when manufacturing a film with a wider width, the haze of the film increases if the width of the shrinkage of the width is too large to secure the product width or the tenter stretch ratio is increased to secure the product width. In addition, the width of the variation in the transmittance (CNT) in the crossed Nicol state related to it is expanded, and when this film is used as a polarizing plate, the contrast decreases due to an increase in haze, and the brightness unevenness due to the CNT variation. Will occur. In addition, when the film is stretched excessively, the risk of the film tearing and breaking from the stretched clip sandwiching the web is greatly increased, so in the production of a wide film, shrinkage of the film width due to roll condensation is a major problem. Become.

  Due to the above problems, the film portion where condensation occurs is compared with the film portion where it does not generate a difference in the retardation value, the haze increases, or the transmittance in the crossed Nicol state. As a result, (CNT) rises, resulting in a decrease in contrast when the liquid crystal panel is formed. Furthermore, even when post-processing such as applying an antireflection layer, a hardened surface layer, etc. to the surface of the optical film, the wettability is different from the surrounding film part, causing a failure to repel the coating liquid, Or an application layer tends to become uneven.

  As described above, the generation of condensation due to the additive vapor or the like occurs when the atmospheric gas including the additive vapor or the like passes between zones having different drying temperatures (atmospheric temperatures). For example, when the atmospheric gas flows from the high temperature zone to the low temperature zone, condensation of the additive vapor that is below the dew point is likely to occur on the inner wall around the inlet of the low temperature zone and the surface of the transport roll. Conversely, even when atmospheric gas containing additive vapor flows from the low temperature zone to the high temperature zone, the inner wall around the inlet of the high temperature zone and the transport roll are cooled by the atmospheric gas from the low temperature zone, and the additive vapor is Condensation is likely to occur below the dew point.

  In addition, in the zone where the amount of residual solvent in the web is large, the additive tends to volatilize due to the interaction with the solvent molecules that evaporate. Particularly, in the drying zone or the tenter zone immediately after peeling from the support, the residual solvent rapidly Due to proper evaporation, the film temperature of the web is lowered, the temperature of the transport roll is also lowered, and condensation is likely to occur.

  In order to prevent such problems, it is sufficient to select and use additives that have high vapor pressure and are less likely to volatilize, but search for additive compounds with extremely low volatility while satisfying the various properties required for optical films. That is very difficult.

  By the way, as shown in FIG. 8, for example, in the conventional solution casting film forming apparatus, air curtains (13) and (13) are installed between the drying zones, and the flow of atmospheric gas is shielded from the transport web (14). However, a sufficient effect was not always obtained.

  In addition, there is a method to increase the supply air volume to the drying zone and lower the additive vapor concentration, but it requires air conditioning equipment with a very large capacity, which increases equipment costs and also increases running costs and energy consumption. .

  In addition, in order to prevent condensation of the additive vapor to the transport roll, a roll with a heating medium flowing inside the roll or a heater is also commercially available, but due to its structure, the roll diameter and weight are large and can be installed. The place is limited and the exchange takes time. Further, such a heating roll is expensive, and it is not practical to introduce a large number of expensive heating rolls into a transport roll that is frequently replaced periodically due to scratches or surface wear.

  Also, when the generation (attachment) of condensation of additive vapor was confirmed on the film, production was stopped, the location where the condensation occurred and the transport roll on the downstream side were cleaned, and the film was manufactured before production was stopped. For optical film products, it is checked whether or not the surface contamination due to condensation of additive vapor starts from any lot and it is unusable as a product by unwinding the wound film. There was a problem that a factor such as excision was required and the factory operation rate was greatly reduced.

  An object of the present invention is to solve the above-mentioned problems of the prior art, and to improve the productivity by preventing the generation of condensation such as additive vapor in the method of producing an optical film by the solution casting film forming method.

  In addition, the purpose of the present invention is to produce an optical film that does not cause deterioration of quality such as wrinkles and slippage due to variation in peelability, variation in retardation, etc. An object of the present invention is to provide an optical film capable of meeting the demand for higher quality, a manufacturing method thereof, a polarizing plate using the optical film, and a display device.

  In order to achieve the above object, the invention of claim 1 is characterized in that a resin solution (dope) containing a thermoplastic resin, an organic solvent, and an additive is cast from a casting die onto a metal support. A casting zone (A) for forming a film (web) and peeling the web from the support, a stretching zone (B) for stretching the web with a tenter, and a drying zone (C) for drying the web are provided. Production of an optical film by a solution casting method in which either one of a stretching zone (B) and a drying zone (C) is disposed after the stretching zone (A) and then the other is disposed. In the method, when the web is sequentially passed through the inter-zone transition between zones having different atmospheric temperatures, the transition between any one of the inter-zone transitions to which the web migrates, or between all the zones UV irradiation at transition Established the location and / or atmospheric plasma apparatus, the web to migrate transition between zones, it is characterized in that ultraviolet radiation and / or plasma irradiation.

  Invention of Claim 2 is a manufacturing method of the optical film of Claim 1, Comprising: The difference of the atmospheric temperature between the zones from which atmospheric temperature differs is a range of 10 to 120 degreeC. It is a feature.

  The invention of claim 3 is the method of manufacturing an optical film according to claim 1 or 2, wherein the thermoplastic resin is a cellulose ester resin.

  The invention of an optical film according to claim 4 is manufactured by the method for manufacturing an optical film according to any one of claims 1 to 3.

  The invention of a polarizing plate according to claim 5 is characterized in that the optical film according to claim 4 is provided on at least one surface.

  The invention of a display device according to a sixth aspect uses the polarizing plate according to the fifth aspect.

  According to the first aspect of the present invention, a resin solution (dope) containing a thermoplastic resin, an organic solvent, and an additive is cast on a metal support from a casting die to form a casting film (web) and support. It is provided with a casting zone (A) for peeling the web from the body, a stretching zone (B) for stretching the web with a tenter, and a drying zone (C) for drying the web, and after the casting zone (A), stretching In the method for producing an optical film by the solution casting film forming method in which one of the zone (B) and the drying zone (C) is disposed and then the other is disposed, When sequentially passing through the inter-zone transition between different zones, any one of the inter-zone transitions or all inter-zone transitions among the inter-zone transitions to which the web transitions are provided. Or atmospheric pressure plasm The apparatus is installed to irradiate the web that moves between the zone transition portions with ultraviolet irradiation and / or plasma irradiation. According to the invention of claim 1, the atmospheric pressure plasma device or the At least one of the ultraviolet irradiation devices is installed, and the additive volatile vapor that flows through the zone transition portion as the web moves by irradiating the web moving through the zone transition portion with ultraviolet rays and / or plasma. Can be decomposed into carbon dioxide, water, etc. to prevent the generation of condensation.

  This also suppresses shrinkage in the width direction of the web, making it possible to manufacture an ultra-wide optical film having a product width of 2000 mm or more.

  Furthermore, in order to obtain the necessary retardation value by suppressing the width shrinkage in the past, in the retardation film that had to be stretched at a high stretching rate with a tenter in the stretching zone, the retardation was released after peeling from the metal support. Since it is determined by the total expansion ratio in the MD direction (conveyance direction) and TD direction (width direction) of the film until it becomes a product, when the width shrinks before the tenter of the stretching zone, the width by the tenter that compensates for that amount Since stretching in the hand direction is required, troubles such as breaking of the web were likely to occur, but according to the present invention, the stretching ratio in the tenter of the stretching zone can be lowered by suppressing the width shrinkage of the web, The risk of breakage can also be avoided. As a result, the haze of the web can be lowered, and the contrast of the display panel when the polarizing plate is obtained can be increased.

  Due to the above-described effects of the present invention, a method for producing an optical film that can meet the demands for thinning, widening, and improving the quality of an optical film as a protective film for a polarizing plate and the like, and the method Can provide a high-quality optical film, a polarizing plate using the optical film, and a display device.

  Next, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

  FIG. 1 is a flow sheet showing a first embodiment of an apparatus for producing an optical film of the present invention by a solution casting film forming method.

  In the figure, the method for producing an optical film according to the present invention involves casting a resin solution (dope) containing a thermoplastic resin, an organic solvent, and an additive from a casting die (1) onto a metal support (2). A casting zone (A) for forming a casting membrane (web) (4) and peeling the web (4) from the support (2), and a stretching zone (B) for stretching the web (4) with a tenter. And a drying zone (C) for drying the web (4), after the casting zone (A), one of the stretching zone (B) and the drying zone (C) is disposed, and thereafter The other is arranged.

  And in the manufacturing method of the optical film of this invention, when letting a web (4) pass through the transition part between zones between zones from which atmospheric temperature differs sequentially, among the transition parts between zones to which a web (4) transfers. In any one of the zone-to-zone transition parts, or all the zone-to-zone transition parts, the ultraviolet irradiation device (5) and / or the atmospheric pressure plasma device (6) is installed, and the web that migrates between the zone transition parts, Irradiation with ultraviolet rays and / or plasma irradiation.

  In the embodiment shown in FIG. 1, the stretching zone (B) is disposed after the casting zone (A), and the drying zone (C) is disposed after the stretching zone (B). Then, when the web (4) is sequentially passed through the zone-to-zone transition between the zones having different atmospheric temperatures, the zone-to-zone transition between the casting zone (A) and the stretching zone (B) adjacent thereto. An ultraviolet irradiation device (5) and / or an atmospheric pressure plasma device (6) is installed in the section (21), and the web (4) moving through the inter-zone transition section (21) is irradiated with ultraviolet irradiation and / or plasma. To do.

  In the embodiment shown in FIG. 2, as in the case of FIG. 1 above, the stretching zone (B) is arranged after the casting zone (A), and the drying zone (C) is further placed after the stretching zone (B). Although it is arranged, when the web (4) is sequentially passed through the zone-to-zone transition part between the zones having different atmospheric temperatures, it is between the casting zone (A) and the drawing zone (B) adjacent thereto. The ultraviolet irradiation device (5) and / or the normal zone transition part (21) and the zone transition part (22) between the stretching zone (B) and the drying zone (C) adjacent thereto, respectively. A pressure plasma apparatus (6) is installed, and ultraviolet irradiation and / or plasma irradiation are performed on the web (4) that moves through the inter-zone transition portions (21) and (22), respectively.

  In the embodiment shown in FIGS. 1 and 2, the stretching zone (B) is disposed after the casting zone (A), and the drying zone (C) is disposed after the stretching zone (B). Not limited to this, in the present invention, after the casting zone (A), either one of the stretching zone (B) and the drying zone (C) is disposed, and then the other is disposed. If it is good.

  Therefore, although illustration is omitted, for example, after the casting zone (A), (a) casting zone (A) → drying zone (C) → drawing zone (B), (b) casting zone (A) → First drying zone (C1) → Stretching zone (B) → Second drying zone (C2), (C) Casting zone (A) → First drying zone (C1) → First stretching zone (B1) → First In order to control the physical properties of the web (4) such as 2 drying zone (C2) → second stretching zone (B2), they may be combined in various orders.

  And the manufacturing method of the optical film by this invention is applied also to embodiment shown in FIG.1 and FIG.2 and embodiment in any case including said (i)-(c), and atmospheric temperature of At least one of a normal pressure plasma apparatus (5) and an ultraviolet irradiation apparatus (6) is installed in a transition part between different zones, and ultraviolet irradiation and / or plasma irradiation is applied to the web (4) that moves through the transition part between zones. By doing so, the additive volatile vapor flowing through the transition zone between zones with the transition of the web (4) can be decomposed into carbon dioxide, water, etc., and the generation of condensation can be prevented.

  Moreover, in the manufacturing method of the optical film of this invention, it is preferable that the difference of the atmospheric temperature between the zones from which atmospheric temperature differs in the above cases is the range of 10 degreeC or more and 120 degrees C or less.

  Further, according to the method for producing an optical film of the present invention, in any of the above cases, shrinkage of the width of the web is suppressed, and an ultra-wide optical film having a product width of 2000 mm or more can be produced. In addition, in order to obtain the necessary retardation value by suppressing the width shrinkage in the past, in the retardation film that had to be stretched at a high stretching rate with a tenter in the stretching zone, the retardation was released after peeling from the metal support. Because it is determined by the total expansion / contraction ratio in the MD direction (conveyance direction) and TD direction (width direction) until it becomes a product, when the width shrinks before the tenter in the stretching zone, it is necessary to compensate for that amount. Although troubles such as breakage were likely to occur, the tenter stretching ratio could be lowered by suppressing the width shrinkage, and the risk of breakage could be avoided. Thereby, the haze of the web can also be lowered, and the contrast of the panel when it is made a polarizing plate can be raised.

  By the above effects, an optical film manufacturing method, an optical film, a polarizing plate, and a display device that can meet demands for thinning, widening, and high quality of a protective film for a polarizing plate and obtain high productivity are provided. Can do.

  Hereinafter, the manufacturing method of the optical film by this Embodiment shown in FIG. 1 is described in detail. The optical film can be produced by a solution casting film forming method.

  In the figure, a dope is cast from a casting die (1) on a metal support (2) made of a rotationally driven endless belt made of, for example, stainless steel, which is transferred indefinitely.

  The dope casting by the casting die (1) includes a doctor blade method in which the film thickness of the cast dope film (web) is adjusted with a blade, or a reverse roll coater method in which the film is adjusted with a reverse rotating roll. However, it is preferable to use a pressure die that can adjust the slit shape of the die part and easily make the film thickness uniform. Examples of the pressure die include a coat hanger die and a T die, and any of them is preferably used. The casting die (1) is usually provided with a decompression chamber (not shown).

  Here, the solid content concentration of the cellulose ester solution (dope) is preferably 15 to 30% by mass. If the solid content concentration of the cellulose ester solution (dope) is less than 15% by mass, sufficient drying cannot be performed on the metal support (2), and a part of the dope film is on the metal support (2) at the time of peeling. This leads to belt contamination and is not preferable. Also, if the solid content concentration exceeds 30%, the dope viscosity increases, the filter clogging becomes faster in the dope adjustment process, or the pressure increases during casting on the metal support (2), and cannot be extruded. It is not preferable.

  In the illustrated film forming apparatus having a rotationally driven endless belt as the metal support (2), the metal support (2) includes a pair of front and rear winding drums (9) and (9) and a plurality of intermediate rolls (not shown). ). Driving to apply tension (not shown) to the belt metal support (2) to one or both of the winding drums (9) and (9) at both ends of the metal support (2) made of a rotationally driven endless belt. An apparatus is provided, whereby the metal support (2) is used in a tensioned state.

  The width of the metal support (2) is preferably 1700 to 2400 mm, the casting width of the cellulose ester solution is preferably 1600 to 2500 mm, and the width of the film after winding is preferably 1400 to 2500 mm. Thereby, the wide optical film for liquid crystal display devices can be manufactured by a metal support body system.

  Moreover, it is preferable that the moving speed of a metal support body (2) is 40-200 m / min.

  When an endless belt is used as the metal support (2), the belt temperature during film formation is a general temperature range of 0 ° C. to a temperature lower than the boiling point of the solvent, and the mixed solvent is lower than the boiling point of the lowest boiling solvent. The film can be cast at a temperature, and more preferably in the range of 5 ° C to the boiling point of the solvent-5 ° C. At this time, it is necessary to control the ambient atmospheric humidity above the dew point.

  The dope cast on the surface of the metal support (2) as described above also increases the strength (film strength) of the gel film by promoting drying until stripping.

  In the system using an endless belt as the metal support (2), on the metal support (2), the web (4) has a film strength that can be peeled from the metal support (2) by the peeling roll (3). In order to dry and solidify, it is preferable to dry to 150 mass% or less of the residual solvent amount in a web (4), and 70-130 mass% is more preferable. Moreover, as for web temperature when peeling a web (4) from a metal support body (2), 0-30 degreeC is preferable. In addition, immediately after the web (4) is peeled off from the metal support (2), the temperature once decreases rapidly due to the solvent evaporation from the metal support (2) contact surface side, and vapors such as water vapor and solvent vapor in the atmosphere are volatilized. Since the sex component tends to condense, the web temperature during peeling is more preferably 5 to 30 ° C.

  Here, the residual solvent amount can be expressed by the following equation.

Residual solvent amount (% by mass) = {(MN) / N} × 100
In the formula, M is a mass at an arbitrary point of the web, and N is a mass when a mass M is dried at 110 ° C. for 3 hours.

  The dope film (web) (4) formed by the dope cast on the metal support (2) is heated on the metal support (2), and the release roll (3) from the metal support (2). Until the web is peelable.

  In order to evaporate the solvent, there are a method of blowing air (7) from the web side, a method of transferring heat from the back surface of the metal support (2) by a liquid, a method of transferring heat from the front and back by radiant heat, etc. It may be used alone or in combination.

  In the system using an endless belt for the metal support (2), the peeling tension when the web (4) is peeled from the metal support (2) by the peeling roll (3) is measured by a peeling force as in JIS Z 0237. Peeling with a larger tension than the peeling force obtained in, but this may cause the peeling position to be taken downstream if the peeling tension is equal to the peeling force obtained by the JIS measurement method during high-speed film formation. Therefore, it goes higher for stabilization. Even if the film is formed with the same peel tension in the process, it has been confirmed that the variation of the crossed Nicols transmittance (CNT) of the film is greatly reduced when the peel force by the JIS measurement method is lowered.

  As a peeling tension value in the process, when preparing a retardation film that requires a high retardation value, the web after peeling from the support is prevented from extending in the MD direction due to the conveyance tension (extends in the MD direction). When the film is stretched in the TD direction by a subsequent tenter, it is difficult to raise the desired retardation value), and in other applications, peeling is performed at a high tension of about 300 N / m from a low tension of about 50 N / m.

  FIG. 3 is a flow sheet showing a third embodiment of the apparatus for carrying out the method for producing an optical film by the solution casting film forming method in the present invention. As a metal support, for example, a super chrome hard chrome plating on the surface The case where the stainless steel rotational drive drum (10) which performed the process is used is illustrated.

  The other points of the optical film manufacturing apparatus in FIG. 3 are the same as those in the case of the optical film manufacturing apparatus in FIG.

  In the method for producing an optical film according to the embodiment of the present invention shown in FIGS. 1 to 3, an ultraviolet irradiation device (5) or a normal pressure plasma device (6) is applied to the zone transition portions (21) and (22) having different temperatures. The additive vapor volatilized from the web (4) is decomposed into carbon dioxide or water, and the surface of the web (4) is also modified.

  Here, the temperature difference between the zone transition portions (21) and (22) is preferably in the range of 10 ° C to 120 ° C. When the temperature difference is less than 10 ° C., condensation hardly occurs, so there is no need to install atmospheric pressure plasma or ultraviolet irradiation device that requires equipment and running costs. Further, if there is a temperature difference of 120 ° C. or more, the web will be wrinkled or distorted due to heat shrinkage or the like, and a product with good flatness cannot be obtained.

  Moreover, in the apparatus which implements the manufacturing method of the optical film shown in FIGS. 1 to 3, the stretching process is performed by fixing both side edges of the web (4) with clips or the like when manufacturing the film for a liquid crystal display device. The tenter method is preferable in order to improve the flatness and dimensional stability of the film.

  It is preferable that the residual solvent amount of the web (4) immediately before entering the tenter of the stretching zone (B) is 2 to 100% by mass.

  In the present embodiment, the stretch ratio of the web (4) in the tenter in the stretching zone (B) is 1.03 to 2, preferably 1.05 to 1.8, and more preferably 1.05. It is desirable that it is 1.6 times. Moreover, the temperature of the warm air blown from the warm air blowing slit port in the tenter in the stretching zone (B) is 20 to 200 ° C, preferably 40 to 190 ° C, and more preferably 60 to 180 ° C.

  In the drying zone (C) provided on the back side of the tenter in the stretching zone (B), the film (web) (11) is meandered by a plurality of conveying rolls arranged in a staggered manner as viewed from the side, The film (11) is to be dried. The film transport tension in the drying zone (C) is affected by the physical properties of the dope, the amount of residual solvent in the peeling and film transport process, the drying temperature, etc., but the film transport tension during drying is 10 mm wide. 0.3 to 3N per unit, and 0.4 to 2.7N is more preferable.

  The means for drying the web (4) is not particularly limited, and is generally performed with hot air, infrared rays, a heating roll, microwaves, or the like. It is preferable to dry with hot air from the viewpoint of simplicity. For example, it is dried by the dry air (7) blown from the hot air inlet at the rear part of the ceiling of the drying zone (C), and is dried at the bottom of the drying zone (C). It is dried by exhaust air being discharged from the outlet of the front portion. The temperature of the drying air (7) is preferably 40 to 160 ° C., more preferably 50 to 150 ° C. in order to improve flatness and dimensional stability.

  These steps from casting to post-drying may be performed in an air atmosphere or in an inert gas atmosphere such as nitrogen gas. In this case, it goes without saying that the dry atmosphere is carried out in consideration of the explosion limit concentration of the solvent.

  For example, a cellulose ester film that has finished the transport drying process is generally subjected to a process of forming an emboss on the film by an embossing apparatus (not shown) in the previous stage of introduction into the winding process.

  Here, the height h (μm) of the emboss is set in the range of 0.05 to 0.3 times the film thickness T, and the width W is set in the range of 0.005 to 0.02 times the film width L. . Embossing may be formed on both sides of the film. In this case, the height h1 + h2 (μm) of the emboss is set in the range of 0.05 to 0.3 times the film thickness T, and the width W is set in the range of 0.005 to 0.02 times the film width L. . For example, when the film thickness is 40 μm, the embossing height h 1 + h 2 (μm) is set to 2 to 12 μm. The emboss width is set to 5 to 30 mm.

  The film (11) that has been dried is taken up by the take-up device (8) to obtain the original roll of the optical film. The film (11) having good dimensional stability can be obtained by setting the residual solvent amount of the film (11) to be dried to 0.5% by mass or less, preferably 0.1% by mass or less.

  For winding the film (11), a commonly used winder may be used, and there are methods for controlling the tension such as a constant torque method, a constant tension method, a taper tension method, a program tension control method with a constant internal stress. You can use them properly.

  The film (11) may be joined to the winding core (winding core) by either a double-sided adhesive tape or a single-sided adhesive tape.

  In the optical film according to this embodiment, the width of the film after winding is preferably 1,400 to 2,500 mm.

  FIG. 4 is an explanatory diagram for explaining the principle of the excimer ultraviolet irradiation device.

  In addition, FIG. 4 shows the case where the excimer ultraviolet irradiation device (5) is installed on both upper and lower sides of the web (4). In the figure, (u) is an excimer ultraviolet lamp, (r) is a reflector, (p) is a purge gas, (q) is quartz glass, and (d) is a gap from the excimer ultraviolet lamp (u) to the web (4). It is.

  In the present embodiment, various ultraviolet irradiation apparatuses can be used, and the wavelength is particularly preferably 250 nm or less. Under such ultraviolet irradiation, the oxygen contained in the purge gas (p) generates active oxygen and ozone, decomposes the volatile vapor of the additive into carbon dioxide, water, etc. together with the ultraviolet rays, and also the surface of the web (4). It is to be reformed.

  Also, if the gap (d) between the ultraviolet lamp (u) and the web (4) is too close, the web will come into contact with the ultraviolet lamp device due to the curl of the web, etc., and the web will be scratched. Is absorbed by oxygen and the volatile vapor of the additive cannot be decomposed and the surface of the web cannot be sufficiently modified. Therefore, the thickness is preferably about 1 to 20 mm, and more preferably 2 to 15 mm. It is desirable to provide an exhaust device near the ultraviolet irradiation device to exhaust the decomposition gas.

  In addition, as shown in FIG. 5, the excimer ultraviolet irradiation device (5) may be installed only on the upper side of the web (4).

(Description of atmospheric pressure plasma)
6 and 7 are explanatory views for explaining the structure of the atmospheric pressure plasma apparatus.

  In general, in an atmospheric pressure plasma apparatus, a reactive gas is made into a plasma state by applying a high-frequency voltage between opposing electrodes to discharge it, whereby the additive volatile vapor of the web is converted into carbon dioxide or water. It decomposes and modifies the web surface.

  The atmospheric pressure plasma method is roughly divided into two types. One is called a direct method or a planar method. A high-frequency power is applied between electrodes arranged opposite to each other so as to sandwich an object to be processed. Is converted into plasma. Another method is called a remote method or a downstream method, in which a reactive gas is introduced through an electrode to which a high-frequency voltage is applied and is turned into plasma. Any of the above schemes can be used in the present invention.

  FIG. 6 shows an atmospheric pressure plasma apparatus of the type called the direct method or the planar method. FIG. 7 shows an atmospheric pressure plasma apparatus of the type called the above-described remote system or downstream system.

  6 and 7, (a) and (b) are counter electrodes of the atmospheric pressure plasma apparatus, (g) is a reactive gas, and (d) is a gap from the plasma injection slit to the surface of the web (4).

  As a simple structure of the atmospheric pressure plasma apparatus in FIG. 6 and FIG. 7, a reactive gas (g) is introduced between the counter electrodes (a) and (b) to which a high-frequency voltage is applied, and is made to pass through to form a plasma. (4) The surface treatment film is formed by spraying the surface.

  In the present embodiment, it is necessary to employ an electrode capable of applying such a high power voltage and maintaining a uniform glow discharge state in the atmospheric pressure plasma apparatus.

  Such an electrode is preferably a metal base material coated with a dielectric. It is preferable to coat a dielectric on at least one side of the opposed application electrode and the ground electrode, and more preferably coat both of the opposed application electrode and the ground electrode with a dielectric. The dielectric is preferably an inorganic substance having a relative dielectric constant of 6 to 45. Examples of such a dielectric include ceramics such as alumina and silicon nitride, silicate glass, borate glass, and the like. Glass lining material and the like.

  In addition, when a cellulose ester film, which is a transparent film base material, is placed between electrodes or transported between electrodes and exposed to plasma, the transparent film base material has a roll electrode specification that can be transported in contact with one electrode. In addition, the dielectric surface is polished and the electrode surface roughness Rmax (specified in JIS B 0601) is 10 μm or less to keep the dielectric thickness and the gap between the electrodes constant. It is possible to stabilize the discharge state, eliminate distortion and cracking due to thermal shrinkage difference and residual stress, and greatly improve durability by covering with non-porous high precision inorganic dielectric. preferable.

  On the other hand, if the gap (d) between the blow-out slit for supplying the plasma and the surface of the web (4) is too close, the web curls or the like and comes into contact with the atmospheric pressure plasma apparatus to create a scratch on the web. If it is too far away, the radicals of the plasma will not reach sufficiently, and volatile vapor decomposition of the additive and the modification of the web surface will not be sufficient, so 1-30 mm is preferable, and 2-20 mm is more preferable.

  Various materials such as nitrogen, oxygen, argon, and helium can be used as the source gas (g), but nitrogen is preferable from the viewpoints of the environment, exhaust aftertreatment, and running cost. Furthermore, it is more preferable to mix a small amount of oxygen with nitrogen. The mixing ratio of oxygen is preferably 5% by volume or less with respect to the volume of the source gas.

  The source gas flow rate of atmospheric pressure plasma is preferably 20 to 5000 L / min per 1 m of plasma width. Furthermore, 40-2500 L / min is more preferable. In addition, it is desirable to exhaust the cracked gas by providing an exhaust device near the atmospheric pressure plasma device.

  In the present embodiment, the dope for producing an optical film contains a resin such as a cellulose ester resin as a main material, and includes a plasticizer, a retardation adjusting agent, an ultraviolet absorber, fine particles, and a low molecular weight substance. Including at least one kind of substance and a solvent.

  Hereinafter, these will be described.

  In the method for producing an optical film of the present embodiment, various resins can be used as the film material, and among them, cellulose ester is preferable.

  A cellulose ester is a cellulose ester in which a hydroxyl group derived from cellulose is substituted with an acyl group or the like. Examples thereof include cellulose acylates such as cellulose acetate, cellulose triacetate, cellulose acetate propionate, cellulose acetate butyrate and cellulose acetate propionate butyrate, and cellulose acetate having an aliphatic polyester graft side chain. Among these, cellulose acetate, cellulose acetate propionate, and cellulose acetate having an aliphatic polyester graft side chain are preferable. Other substituents may be included as long as the effects of the present embodiment are not impaired.

  As an example of cellulose triacetate, the substitution degree of acetyl groups is preferably 2.0 or more and 3.0 or less. By setting the degree of substitution within this range, good moldability can be obtained, and desired in-plane retardation (Ro) and thickness direction retardation (Rt) can be obtained. If the substitution degree of the acetyl group is lower than this range, the heat resistance as a retardation film, particularly the dimensional stability under wet heat may be inferior, and if the substitution degree is too large, the necessary retardation characteristics will not be exhibited. There is a case.

  Although there is no limitation in particular as a cellulose of the raw material of the cellulose ester used for this Embodiment, Cotton linter, wood pulp, kenaf etc. can be mentioned. Moreover, the cellulose ester obtained from them can be mixed and used in arbitrary ratios, respectively.

  In the present embodiment, the number average molecular weight of the cellulose ester is preferably in the range of 60,000 to 300,000 because the mechanical strength of the resulting film is strong. Furthermore, 70,000-200,000 are preferable.

  In the present embodiment, various additives can be added to the cellulose ester.

  In the method for producing an optical film according to the present embodiment, it is preferable to use a dope composition containing a cellulose ester and an additive for reducing the thickness direction retardation (Rt).

  In the present embodiment, reducing the thickness direction retardation (Rt) of the cellulose ester film is important in terms of expanding the viewing angle of a liquid crystal display device operating in an IPS (In-Plane-Switching) mode. However, in the present embodiment, examples of the additive for reducing such thickness direction retardation (Rt) include the following.

  In general, retardation of a cellulose ester film appears as the sum of retardation derived from a cellulose ester and retardation derived from an additive. Therefore, an additive for reducing the retardation of the cellulose ester is an additive that disturbs the orientation of the cellulose ester and is difficult to orient itself and / or has a small polarizability anisotropy. It is a compound that effectively reduces it. Therefore, as an additive for disturbing the orientation of the cellulose ester, an aliphatic compound is preferable to an aromatic compound.

  Here, as a specific retardation reducing agent, for example, a polyester represented by the following general formula (1) or (2) may be mentioned.

B1- (GA-) mG-B1 (1)
B2- (GA-) nG-B2 (2)
In the above formula, B1 represents a monocarboxylic acid component, B2 represents a monoalcohol component, G represents a divalent alcohol component, A represents a dibasic acid component, and these are synthesized. B1, B2, G, and A are all characterized by not containing an aromatic ring. m and n represent the number of repetitions.

  There is no restriction | limiting in particular as a monocarboxylic acid component represented by B1, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, etc. can be used.

  Examples of preferable monocarboxylic acid include the following, but the present embodiment is not limited to this.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-12. When acetic acid is contained, the compatibility with the cellulose ester is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

  Preferred monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, tridecylic acid , Saturated fatty acids such as myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, melicic acid, and laccelic acid, undecinic acid, Examples thereof include unsaturated fatty acids such as oleic acid, sorbic acid, linoleic acid, linolenic acid and arachidonic acid.

  The monoalcohol component represented by B2 is not particularly limited, and known alcohols can be used. For example, an aliphatic saturated alcohol or aliphatic unsaturated alcohol having a straight chain or a side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-12.

  Examples of the divalent alcohol component represented by G include the following, but the present embodiment is not limited to this. For example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,5-pentanediol, 1,6- Hexanediol, 1,5-pentylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and the like can be mentioned. Among these, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1 1,2-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol, diethylene glycol, and triethylene glycol are preferred, and 1,3-propylene glycol, 1,4-butylene glycol Lumpur, 1,6-hexanediol, diethylene glycol is preferably used.

  The dibasic acid (dicarboxylic acid) component represented by A is preferably an aliphatic dibasic acid or an alicyclic dibasic acid. Examples of the aliphatic dibasic acid include malonic acid, succinic acid, glutaric acid, and adipic acid. , Pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid and the like, in particular, aliphatic carboxylic acid having 4 to 12 carbon atoms, at least one selected from these To do. That is, two or more dibasic acids may be used in combination.

  The number of repetitions m and n in the above general formula (1) or (2) is preferably 1 or more and 170 or less.

  The weight average molecular weight of the polyester is preferably 20,000 or less, and more preferably 10,000 or less. In particular, polyesters having a mass average molecular weight of 500 to 10,000 have good compatibility with cellulose esters, and neither evaporation nor volatilization occurs in film formation.

  Polycondensation of polyester is carried out by a conventional method. For example, a direct reaction of the dibasic acid and glycol, a hot melt condensation method by the polyesterification reaction or transesterification reaction of the dibasic acid or alkyl esters thereof, for example, a methyl ester of dibasic acid and glycols, or Although it can be easily synthesized by any method of dehydrohalogenation reaction between acid chloride of these acids and glycol, polyesters having a mass average molecular weight not so large are preferably directly reacted. Polyester having a high distribution on the low molecular weight side has a very good compatibility with the cellulose ester, and after forming the film, a moisture permeability is small, and a cellulose ester film rich in transparency can be obtained.

  The method for adjusting the molecular weight is not particularly limited, and a conventional method can be used. For example, although depending on the polymerization conditions, the amount of these monovalent acids or alcohols can be controlled by a method of blocking the molecular ends with monovalent acids or monovalent alcohols. In this case, a monovalent acid is preferable from the viewpoint of polymer stability. For example, acetic acid, propionic acid, butyric acid, etc. can be mentioned, but during the polycondensation reaction, it is not distilled out of the system, but is stopped and such monovalent acid is removed from the reaction system. The one that is easy to accumulate is selected. These may be used in combination. In the case of direct reaction, the mass average molecular weight can also be adjusted by measuring the timing at which the reaction is stopped by the amount of water distilled off during the reaction. In addition, it can be adjusted by biasing the number of moles of glycol or dibasic acid to be charged, or can be adjusted by controlling the reaction temperature.

  It is preferable to contain 1-40 mass% of polyester represented by the said General formula (1) or (2) with respect to a cellulose ester. It is particularly preferable to contain 5 to 15% by mass.

  In this Embodiment, the following are further mentioned as an additive which reduces thickness direction retardation (Rt).

  The dope used in the production of the optical film of the present embodiment is mainly a cellulose ester, a polymer as an additive for reducing retardation (Rt) (a polymer obtained by polymerizing an ethylenically unsaturated monomer, an acrylic polymer) ), And an organic solvent.

  In this embodiment, in order to synthesize a polymer as an additive for reducing the thickness direction retardation (Rt), it is difficult to control the molecular weight in normal polymerization, and the molecular weight can be adjusted as much as possible by a method that does not increase the molecular weight too much. It is desirable to use the method. Such polymerization methods include a method using a peroxide polymerization initiator such as cumene peroxide and t-butyl hydroperoxide, a method using a polymerization initiator in a larger amount than normal polymerization, and a mercapto compound in addition to the polymerization initiator. And a method using a chain transfer agent such as carbon tetrachloride, a method using a polymerization terminator such as benzoquinone and dinitrobenzene in addition to the polymerization initiator, and JP-A No. 2000-128911 or JP-A No. 2000-344823. Examples include a method of bulk polymerization using a compound having one thiol group and a secondary hydroxyl group as described in the publication, or a polymerization catalyst in which the compound and an organometallic compound are used in combination. The method described in the publication is particularly preferable.

  In this Embodiment, although the monomer as a monomer unit which comprises the polymer as an additive which reduces useful thickness direction retardation (Rt) is mentioned below, it is not limited to this.

  As the ethylenically unsaturated monomer unit constituting the polymer as an additive for reducing the thickness direction retardation (Rt) obtained by polymerizing an ethylenically unsaturated monomer, first, as a vinyl ester, for example, vinyl acetate, propionic acid, etc. Vinyl, vinyl butyrate, vinyl valerate, vinyl pivalate, vinyl caproate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl octylate, vinyl methacrylate, Examples include vinyl crotonate, vinyl sorbate, vinyl benzoate, and vinyl cinnamate.

  Next, as acrylate ester, for example, methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate ( n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-), nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), cyclohexyl acrylate, acrylic acid (2-ethylhexyl), benzyl acrylate, phenethyl acrylate, acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl) ), Acrylic acid (2-hydroxypropyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2- Dorokishibuchiru) acrylate-p-hydroxymethylphenyl,-p-acrylic acid (2-hydroxyethyl) phenyl and the like; as methacrylic acid ester, the acrylic acid ester include those changed to methacrylic acid esters.

  Furthermore, examples of the unsaturated acid include acrylic acid, methacrylic acid, maleic anhydride, crotonic acid, itaconic acid, and the like.

  The polymer composed of the above monomers may be a copolymer or a homopolymer, and is preferably a vinyl ester homopolymer, a vinyl ester copolymer, or a copolymer of vinyl ester and acrylic acid or methacrylic acid ester.

  In this embodiment, an acrylic polymer (simply referred to as an acrylic polymer) refers to a homopolymer or copolymer of acrylic acid or alkyl methacrylate having no aromatic ring or a monomer unit having a cyclohexyl group.

  Examples of the acrylate monomer having no aromatic ring and cyclohexyl group include, for example, methyl acrylate, ethyl acrylate, propyl acrylate (i-, n-), butyl acrylate (n-, i-, s-, t-), pentyl acrylate (n-, i-, s-), hexyl acrylate (n-, i-), heptyl acrylate (n-, i-), octyl acrylate (n-, i-) , Nonyl acrylate (n-, i-), myristyl acrylate (n-, i-), acrylic acid (2-ethylhexyl), acrylic acid (ε-caprolactone), acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3-hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid 2-methoxy-ethyl), acrylic acid (2-ethoxyethyl), or the acrylic acid ester may include those obtained by changing the methacrylic acid ester.

  The acrylic polymer is a homopolymer or copolymer of the above-mentioned monomers, but it is preferable that the acrylic acid methyl ester monomer unit has 30% by mass or more, and the methacrylic acid methyl ester monomer unit has 40% by mass or more. It is preferable. In particular, a homopolymer of methyl acrylate or methyl methacrylate is preferred.

  Polymers obtained by polymerizing the above ethylenically unsaturated monomers and acrylic polymers are both highly compatible with cellulose ester, excellent in productivity without evaporation and volatilization, and retainability as a protective film for polarizing plates The moisture permeability is small, and the dimensional stability is excellent.

  In the present embodiment, an acrylic acid or methacrylic acid ester monomer having a hydroxyl group is not a homopolymer but a constituent unit of a copolymer. In this case, it is preferable that the acrylic acid or methacrylic acid ester monomer unit having a hydroxyl group is contained in an acrylic polymer in an amount of 2 to 20% by mass.

  In the method for producing an optical film of the present embodiment, the dope composition comprises a cellulose ester and an acrylic polymer having a mass average molecular weight of 500 or more and 3,000 or less as an additive for reducing thickness direction retardation (Rt). It is preferable to contain.

  Moreover, in the manufacturing method of the optical film of this Embodiment, dope composition is acrylic ester with a mass average molecular weight of 5,000 or more and 30,000 or less as an additive which reduces cellulose ester and thickness direction retardation (Rt). It is preferable that it contains a polymer.

  In the present embodiment, a polymer having a mass average molecular weight of 500 or more and 3,000 or less as an additive for reducing thickness direction retardation (Rt), or a polymer having a mass average molecular weight of 5,000 or more and 30,000 or less If so, the compatibility with the cellulose ester is good, and neither evaporation nor volatilization occurs during film formation. Moreover, the transparency of the cellulose ester film after film formation is excellent, the moisture permeability is extremely low, and it exhibits excellent performance as a protective film for polarizing plates.

  In this Embodiment, the polymer which has a hydroxyl group in a side chain can also be preferably used as an additive which reduces thickness direction retardation (Rt). The monomer unit having a hydroxyl group is the same as the monomer described above, but acrylic acid or methacrylic acid ester is preferable. For example, acrylic acid (2-hydroxyethyl), acrylic acid (2-hydroxypropyl), acrylic acid (3 -Hydroxypropyl), acrylic acid (4-hydroxybutyl), acrylic acid (2-hydroxybutyl), acrylic acid-p-hydroxymethylphenyl, acrylic acid-p- (2-hydroxyethyl) phenyl, or these acrylic acids. Examples include those substituted with methacrylic acid, preferably 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate. The acrylic acid ester or methacrylic acid ester monomer unit having a hydroxyl group in the polymer is preferably contained in the polymer in an amount of 2 to 20% by mass, more preferably 2 to 10% by mass.

  Those containing 2 to 20% by mass of the monomer unit having the hydroxyl group as described above, of course, have excellent compatibility with cellulose ester, retention, dimensional stability, and low moisture permeability. It is particularly excellent in adhesion with a polarizer as a protective film for a polarizing plate, and has an effect of improving the durability of the polarizing plate.

  In the present embodiment, it is preferable that at least one terminal of the main chain of the polymer has a hydroxyl group. The method of having a hydroxyl group at the end of the main chain is not particularly limited as long as it has a hydroxyl group at the end of the main chain, but radical polymerization having a hydroxyl group such as azobis (2-hydroxyethylbutyrate). A method of using an initiator, a method of using a chain transfer agent having a hydroxyl group such as 2-mercaptoethanol, a method of using a polymerization terminator having a hydroxyl group, a method of having a hydroxyl group at the terminal by living ion polymerization, Using a polymerization catalyst in which a compound having one thiol group and a secondary hydroxyl group as disclosed in JP-A No. 2000-128911 or JP-A No. 2000-344823, or a combination of the compound and an organometallic compound is used. It can be obtained by a polymerization method or the like, and the method described in the publication is particularly preferable. The polymer produced by the method related to the description in this publication is commercially available as Act Flow Series manufactured by Soken Chemical Co., Ltd., and can be preferably used.

  In the present embodiment, the polymer having a hydroxyl group at the terminal and / or the polymer having a hydroxyl group in the side chain has an effect of significantly improving the compatibility and transparency of the polymer with respect to the cellulose ester.

  In the present embodiment, as an additive for reducing useful thickness direction retardation (Rt), in addition to the above, for example, an ester compound of diglycerin polyhydric alcohol and fatty acid described in JP-A-2000-63560 An ester or ether compound of a hexose sugar alcohol described in JP-A No. 2001-247717, a trialiphatic alcohol phosphate compound described in JP-A No. 2004-315613, and a general formula described in JP-A No. 2005-41911 ( 1), a phosphate ester compound described in JP-A No. 2004-315605, a styrene oligomer described in JP-A No. 2005-105139, and a polymer of a styrene monomer described in JP-A No. 2005-105140. Can be mentioned.

  Moreover, in this Embodiment, the additive which reduces thickness direction retardation (Rt) can be found also with the following method.

  A dope formulation in which cellulose ester is dissolved in a mixed organic solvent composed of methyl acetate and acetone is formed on a glass plate and dried at 120 ° C./15 min to produce a cellulose ester film having a thickness of 80 μm. The retardation in the thickness direction of the cellulose ester film is measured, and this is defined as Rt1.

  Next, 10% by mass of the polymer additive is added to the cellulose ester and dissolved in a mixed organic solvent composed of methyl acetate and acetone to prepare a dope formulation. A cellulose ester film with a film thickness of 80 μm is prepared in the same manner as above with this dope formulation. The retardation in the thickness direction of the cellulose ester film is measured, and this is defined as Rt2.

And the relationship of retardation in the thickness direction of the above two cellulose ester films,
Rt2 <Rt1
Then, it can be said that the polymer additive added to the cellulose ester is an additive for reducing the thickness direction retardation (Rt).

  In the present embodiment, the thickness direction retardation (Rt) of the cellulose ester film is −10 nm to +10 nm, preferably −5 nm to +5 nm. Here, in any case where the thickness direction retardation (Rt) of the cellulose ester film is smaller than −10 nm or larger than +10 nm, the viewing angle is narrowed, and the effect of the present embodiment does not appear.

  In the present embodiment, the in-plane retardation (Ro) of the cellulose ester film is 0 nm to +5 nm, preferably 0 nm to +2 nm, more preferably 0 nm to +1 nm, and particularly preferably about 0 nm. Here, in either case where the in-plane retardation (Ro) is smaller than 0 nm or larger than +5 nm, the viewing angle becomes narrow and the effect of the present embodiment does not appear.

  In the optical film of the present embodiment, the in-plane retardation (Ro) defined by the following formula is 30 to 300 nm under the conditions of a temperature of 23 ° C. and a humidity of 55% RH, and the thickness direction retardation (Rt) is a temperature of 23 ° C. It is preferably 70 to 400 nm under the condition of humidity 55% RH.

  The content of the additive for reducing the thickness direction retardation (Rt) described above is preferably 5 to 25% by mass with respect to the cellulose ester resin. If the content of the additive for reducing the thickness direction retardation (Rt) is less than 5% by mass, the effect of reducing the thickness direction retardation (Rt) of the film is not manifested. On the other hand, if the content of the additive for reducing the thickness direction retardation (Rt) exceeds 25% by mass, so-called bleed-out occurs and the stability in the film decreases, which is not preferable.

  In this embodiment, the retardation value of the film is 590 nm at a wavelength of 590 nm under an environment of a temperature of 23 ° C. and a humidity of 55% RH using an automatic birefringence meter KOBRA-21ADH (manufactured by Oji Scientific Instruments). It can be calculated from the obtained refractive indexes Nx, Ny, and Nz by performing a three-dimensional refractive index measurement.

Ro = (Nx−Ny) × d
Rt = ((Nx + Ny) / 2−Nz) × d
In the formula, Nx, Ny, and Nz represent refractive indexes in the principal axes x, y, and z directions of the refractive index ellipsoid (refractive index measured at a wavelength of 590 nm), respectively, and Nx and Ny represent refractive indexes in the in-plane direction of the film. Nz represents the refractive index in the thickness direction of the film. Further, Nx ≧ Ny, and d represents the thickness (nm) of the film.

  In the present embodiment, the cellulose ester film has an angle θ (radian) formed between the slow axis direction and the film forming direction and an in-plane retardation value (Ro) in the following relationship, and particularly a protective film for a polarizing plate, etc. It is preferably used as a cellulose ester film.

P ≦ 1-sin ² (2θ) sin ² (πRo / λ)
Here, P is 0.9999 or less, θ is an angle (° radians) formed between the slow axis direction in the film plane and the film forming direction (straight direction of the film), and λ is the above Nx, Ny, Nz , Θ, the wavelength of light in the three-dimensional refractive index measurement is 590 nm, and π is the circumference.

  In the method for producing an optical film according to the present embodiment, an organic solvent having good solubility with respect to the cellulose derivative is referred to as a good solvent, and exhibits a main effect on dissolution, and an organic solvent used in a large amount among them is used. It is called the main (organic) solvent or the main (organic) solvent.

  Examples of good solvents include ketones such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, ethers such as tetrahydrofuran (THF), 1,4-dioxane, 1,3-dioxolane, 1,2-dimethoxyethane, formic acid Esters such as methyl, ethyl formate, methyl acetate, ethyl acetate, amyl acetate, γ-butyrolactone, methyl cellosolve, dimethylimidazolinone, dimethylformamide, dimethylacetamide, acetonitrile, dimethyl sulfoxide, sulfolane, nitroethane, methylene chloride And 1,3-dioxolane, THF, methyl ethyl ketone, acetone, methyl acetate and methylene chloride are preferable.

  The dope preferably contains 1 to 40% by mass of an alcohol having 1 to 4 carbon atoms in addition to the organic solvent. After the dope is cast on a metal support, the alcohol starts to evaporate and the ratio of the alcohol increases, thereby making the web gel, making the web strong and easy to peel off from the metal support. It is also used as a gelling solvent, and when these ratios are small, it also has a role of promoting the dissolution of the cellulose derivative of the non-chlorine organic solvent.

  Examples of the alcohol having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, tert-butanol, and propylene glycol monomethyl ether. Of these, ethanol is preferred because it has excellent dope stability, has a relatively low boiling point, good drying properties, and no toxicity. These organic solvents alone are not soluble in cellulose derivatives and are called poor solvents.

  The most preferable solvent for dissolving a cellulose derivative, which is a preferable polymer compound satisfying such conditions, at a high concentration is a mixed solvent having a ratio of methylene chloride: ethanol of 95: 5 to 80:20. Alternatively, a mixed solvent having a methyl acetate: ethanol ratio of 60:40 to 95: 5 is also preferably used.

  The film in the present embodiment includes a plasticizer that imparts processability, flexibility, and moisture resistance to the film, fine particles (matting agent) that impart slipperiness to the film, an ultraviolet absorber that imparts an ultraviolet absorbing function, You may contain the antioxidant etc. which prevent deterioration.

  The plasticizer used in the present embodiment is not particularly limited, but a cellulose derivative or a reactive metal compound capable of hydrolytic polycondensation so as not to generate haze, bleed out or volatilize from the film. It preferably has a functional group capable of interacting with the polycondensate of the above by a hydrogen bond or the like.

  Examples of such functional groups include hydroxyl groups, ether groups, carbonyl groups, ester groups, carboxylic acid residues, amino groups, imino groups, amide groups, imide groups, cyano groups, nitro groups, sulfonyl groups, sulfonic acid residues, Examples thereof include a phosphonyl group and a phosphonic acid residue, and a carbonyl group, an ester group and a phosphonyl group are preferred.

  Examples of such plasticizers include phosphate ester plasticizers, phthalate ester plasticizers, trimellitic acid ester plasticizers, pyromellitic acid plasticizers, polyhydric alcohol ester plasticizers, glycolate plasticizers. Agents, citric acid ester plasticizers, fatty acid ester plasticizers, carboxylic acid ester plasticizers, polyester plasticizers, etc. can be preferably used, but polyhydric alcohol ester plasticizers, glycolate plasticizers are particularly preferred. And non-phosphate ester plasticizers such as polycarboxylic acid ester plasticizers.

  The polyhydric alcohol ester is composed of an ester of a dihydric or higher aliphatic polyhydric alcohol and a monocarboxylic acid, and preferably has an aromatic ring or a cycloalkyl ring in the molecule.

  The polyhydric alcohol used in the present embodiment is represented by the following general formula (3).

R ^1- (OH) n (3)
In the formula, R ¹ represents an n-valent organic group, and n represents a positive integer of 2 or more.

Examples of preferred polyhydric alcohols include, but are not limited to, the following.

  Examples of preferred polyhydric alcohols include adonitol, arabitol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, 1, 2-butanediol, 1,3-butanediol, 1,4-butanediol, dibutylene glycol, 1,2,4-butanetriol, 1,5-pentanediol, 1,6-hexanediol, hexanetriol, gallium Examples include lactitol, mannitol, 3-methylpentane-1,3,5-triol, pinacol, sorbitol, trimethylolpropane, trimethylolethane, and xylitol. In particular, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, trimethylolpropane, and xylitol are preferable.

  There is no restriction | limiting in particular as monocarboxylic acid used for the polyhydric alcohol ester of this Embodiment, Well-known aliphatic monocarboxylic acid, alicyclic monocarboxylic acid, aromatic monocarboxylic acid, etc. can be used. Use of an alicyclic monocarboxylic acid or aromatic monocarboxylic acid is preferred in terms of improving moisture permeability and retention.

  Examples of preferred monocarboxylic acids include the following, but are not limited thereto.

  As the aliphatic monocarboxylic acid, a fatty acid having a straight chain or side chain having 1 to 32 carbon atoms can be preferably used. The number of carbon atoms is more preferably 1-20, and particularly preferably 1-10. When acetic acid is contained, the compatibility with the cellulose derivative is increased, and it is also preferable to use a mixture of acetic acid and another monocarboxylic acid.

  Examples of preferred aliphatic monocarboxylic acids include acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, 2-ethyl-hexanecarboxylic acid, undecylic acid, lauric acid, Tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, heptacosanoic acid, montanic acid, mellicic acid, laccellic acid, etc., undecylen Examples thereof include unsaturated fatty acids such as acid, oleic acid, sorbic acid, linoleic acid, linolenic acid, and arachidonic acid.

  Examples of preferred alicyclic monocarboxylic acids include cyclopentane carboxylic acid, cyclohexane carboxylic acid, cyclooctane carboxylic acid, or derivatives thereof.

  Examples of preferred aromatic monocarboxylic acids include those in which an alkyl group is introduced into the benzene ring of benzoic acid such as benzoic acid and toluic acid, and two or more benzene rings such as biphenylcarboxylic acid, naphthalenecarboxylic acid, and tetralincarboxylic acid. Examples thereof include aromatic monocarboxylic acids and derivatives thereof, and benzoic acid is particularly preferable.

  The molecular weight of the polyhydric alcohol ester is not particularly limited, but is preferably 300 to 1,500, and more preferably 350 to 750. A higher molecular weight is preferred because it is less likely to volatilize, and a smaller one is preferred in terms of moisture permeability and compatibility with cellulose derivatives.

  The carboxylic acid used for the polyhydric alcohol ester may be one kind or a mixture of two or more kinds. Moreover, all the OH groups in the polyhydric alcohol may be esterified, or a part of the OH groups may be left as they are.

  The glycolate plasticizer is not particularly limited, but a glycolate plasticizer having an aromatic ring or a cycloalkyl ring in the molecule can be preferably used. As preferred glycolate plasticizers, for example, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl ethyl glycolate and the like can be used.

  For phosphate ester plasticizers, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc. For phthalate ester plasticizers, diethyl phthalate, dimethoxy Ethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate, dicyclohexyl phthalate, etc. can be used, but in this embodiment, it is preferable that substantially no phosphate ester plasticizer is contained. .

  Here, “substantially does not contain” means that the content of the phosphoric ester plasticizer is less than 1% by mass, preferably less than 0.1% by mass, and particularly preferably not added. . These plasticizers can be used alone or in combination of two or more.

  As for the usage-amount of a plasticizer, 1-20 mass% is preferable. 6-16 mass% is further more preferable, Most preferably, it is 8-13 mass%. If the amount of the plasticizer used is less than 1% by mass relative to the cellulose derivative, the effect of reducing the moisture permeability of the film is small, so this is not preferred. If it exceeds 20% by mass, the plasticizer bleeds out from the film, and the film This is not preferable because the physical properties of the resin deteriorate.

  In order to impart slipperiness to the cellulose derivative in the present embodiment, it is preferable to add fine particles such as a matting agent. Examples of the fine particles include fine particles of an inorganic compound or fine particles of an organic compound.

  Examples of the fine particles of the inorganic compound include fine particles of silicon dioxide, titanium dioxide, aluminum oxide, zirconium oxide, tin oxide and the like. Of these, fine particles of a compound containing a silicon atom are preferred, and fine silicon dioxide particles are particularly preferred. Examples of the silicon dioxide fine particles include Aerosil 200, 200V, 300, R972, R972V, R974, R202, R812, R805, OX50, and TT600 manufactured by Aerosil Co., Ltd.

  Examples of the organic compound fine particles include fine particles such as acrylic resin, silicone resin, fluorine compound resin, and urethane resin.

  The primary particle size of the fine particles is not particularly limited, but the average particle size in the film is preferably about 0.05 to 5.0 μm. More preferably, it is 0.1-1.0 micrometer.

  When the cellulose ester film is observed with an electron microscope or an optical microscope, the average particle diameter of the fine particles indicates an average value of the lengths in the major axis direction of the particles at the observation position of the film. As long as the particles are observed in the film, they may be primary particles or secondary particles in which the primary particles are aggregated, but most of the particles that are usually observed are secondary particles.

  As an example of the measurement method, 10 vertical cross-sectional photographs are taken at random for each film, and the number of particles in 100 μm 2 whose major axis length is in the range of 0.05 to 5 μm is counted for each cross-sectional photograph. To do. The average value of the major axis lengths of the particles counted at this time is obtained, and a value obtained by averaging the average values of 10 locations is defined as the average particle size.

  In the case of fine particles, the primary particle size, the particle size after being dispersed in a solvent, and the particle size after being added to the film often change, and what is important is that the fine particles are finally combined with the cellulose ester in the film. And controlling the particle size formed by aggregation.

  Here, when the average particle diameter of the fine particles exceeds 5 μm, haze deterioration or the like may be observed, or a failure may occur in the wound state as a foreign matter. Moreover, when the average particle diameter of fine particles is less than 0.05 μm, it becomes difficult to impart slipperiness to the film.

  The fine particles are used by adding 0.04 to 0.5% by mass with respect to the cellulose ester. Preferably, 0.05 to 0.3% by mass, more preferably 0.05 to 0.25% by mass is used. When the amount of fine particles added is 0.04% by mass or less, the film surface roughness becomes too smooth, and blocking occurs due to an increase in the friction coefficient. If the amount of fine particles added exceeds 0.5% by mass, the coefficient of friction on the film surface will be too low, causing winding misalignment during winding, and the transparency of the film will be low and haze will be high. The above range is essential because it has no value as a film.

  For the dispersion of the fine particles, it is preferable to treat a composition in which the fine particles and the solvent are mixed with a high-pressure dispersion apparatus. The high-pressure dispersion apparatus used in the present embodiment is an apparatus that creates special conditions such as high shear and high-pressure conditions by passing a composition in which fine particles and a solvent are mixed at high speed through a thin tube.

It is preferable that the maximum pressure condition inside the apparatus is 980 N / cm ² or more in a thin tube having a tube diameter of 1 to 2000 μm, for example, by processing with a high-pressure dispersion apparatus. More preferably, the maximum pressure condition inside the apparatus is 1960 N / cm ² or more. At that time, it is preferable that the maximum reaching speed reaches 100 m / sec or more, and the heat transfer speed reaches 4.1840 × 105 J / hr or more.

  Examples of the high-pressure dispersing device as described above include an ultra-high pressure homogenizer (trade name: Microfluidizer) manufactured by Microfluidics Corporation or a nanomizer manufactured by Nanomizer, and other manton gorin type high-pressure dispersing devices such as those manufactured by Izumi Food Machinery. A homogenizer etc. are mentioned.

  In the present embodiment, the fine particles are dispersed in a solvent containing 25 to 100% by mass of a lower alcohol, and then mixed with a dope in which a cellulose ester (cellulose derivative) is dissolved in a solvent, and the mixture is used as a metal support. A cellulose ester film is obtained which is cast on and dried to form a film.

  Here, as a content rate of a lower alcohol, Preferably it is 50-100 mass%, More preferably, it is 75-100 mass%.

  Examples of lower alcohols preferably include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol and the like.

  Although it does not specifically limit as solvents other than a lower alcohol, It is preferable to use the solvent used at the time of film formation of a cellulose ester.

  The fine particles are dispersed in the solvent at a concentration of 1 to 30% by mass. Dispersing at a concentration higher than this is not preferable because the viscosity increases rapidly. The concentration of the fine particles in the dispersion is preferably 5 to 25% by mass, more preferably 10 to 20% by mass.

  The ultraviolet absorbing function of the film is preferably imparted to various optical films such as a polarizing plate protective film, a retardation film, and an optical compensation film from the viewpoint of preventing deterioration of the liquid crystal. For such an ultraviolet absorbing function, a material that absorbs ultraviolet rays may be included in the cellulose derivative, and a layer having an ultraviolet absorbing function may be provided on a film made of the cellulose derivative.

  Examples of ultraviolet absorbers that can be used in the present embodiment include oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and the like. A benzotriazole-based compound with little coloration is preferred. In addition, ultraviolet absorbers described in JP-A-10-182621 and JP-A-8-337574 and polymer ultraviolet absorbers described in JP-A-6-148430 are also preferably used.

  As the ultraviolet absorber, those having excellent absorption ability of ultraviolet rays having a wavelength of 370 nm or less from the viewpoint of preventing deterioration of a polarizer or liquid crystal and those having little absorption of visible light having a wavelength of 400 nm or more from the viewpoint of liquid crystal display properties. preferable.

  Specific examples of ultraviolet absorbers useful in the present embodiment include 2- (2′-hydroxy-5′-methylphenyl) benzotriazole, 2- (2′-hydroxy-3 ′, 5′-di-tert). -Butylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-3 ', 5'-di-tert-butyl Phenyl) -5-chlorobenzotriazole, 2- (2'-hydroxy-3 '-(3 ", 4", 5 ", 6" -tetrahydrophthalimidomethyl) -5'-methylphenyl) benzotriazole, 2,2 -Methylenebis (4- (1,1,3,3-tetramethylbutyl) -6- (2H-benzotriazol-2-yl) phenol, 2- (2'-hydro Cis-3'-tert-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2- (2H-benzotriazol-2-yl) -6- (linear and side chain dodecyl) -4-methylphenol Octyl-3- [3-tert-butyl-4-hydroxy-5- (chloro-2H-benzotriazol-2-yl) phenyl] propionate and 2-ethylhexyl-3- [3-tert-butyl-4-hydroxy Examples include, but are not limited to, a mixture of -5- (5-chloro-2H-benzotriazol-2-yl) phenyl] propionate.

  Further, as commercially available products of ultraviolet absorbers, TINUVIN 109, TINUVIN 171 and TINUVIN 326 (all manufactured by Ciba Specialty Chemicals) can be preferably used.

  Further, as specific examples of the benzophenone-based compound that is an ultraviolet absorber that can be used in this embodiment, 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy- Examples thereof include, but are not limited to, 5-sulfobenzophenone and bis (2-methoxy-4-hydroxy-5-benzoylphenylmethane).

  In this Embodiment, the compounding quantity of these ultraviolet absorbers has the preferable range of 0.01-10 mass% with respect to a cellulose ester (cellulose derivative), Furthermore, 0.1-5 mass% is preferable. If the amount of the ultraviolet absorber used is too small, the ultraviolet absorbing effect may be insufficient. If the amount of the ultraviolet absorber is too large, the transparency of the film may be deteriorated. The ultraviolet absorber is preferably one having high heat stability.

  Moreover, the ultraviolet absorber which can be used for the optical film of this Embodiment is the polymer ultraviolet absorber (or ultraviolet-absorbing polymer) of Unexamined-Japanese-Patent No. 6-148430 and 2002-47357. It can be preferably used. In particular, it is represented by the general formula (1) described in JP-A-6-148430, the general formula (2), or the general formulas (3), (6), and (7) described in JP-A-2002-47357. A polymer ultraviolet absorber is preferably used.

  In general, the antioxidant is also referred to as a deterioration inhibitor, but is preferably contained in a cellulose ester film as an optical film. That is, when a liquid crystal image display device or the like is placed in a high humidity and high temperature state, the cellulose ester film as an optical film may be deteriorated. The antioxidant has a role of delaying or preventing the film from being decomposed by, for example, halogen in the residual solvent in the film or phosphoric acid of the phosphoric acid plasticizer, so that it is preferably contained in the film. .

  As such an antioxidant, a hindered phenol compound is preferably used. For example, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di- -T-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate], 1,6-hexanediol-bis [3 -(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-butylanilino)- 1,3,5-triazine, 2,2-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octa Sil-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N'-hexamethylenebis (3,5-di-t-butyl-4-hydroxy-hydrocinnamamide) 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, tris- (3,5-di-t-butyl-4-hydroxy Benzyl) -isocyanurate and the like. In particular, 2,6-di-t-butyl-p-cresol, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], triethylene glycol-bis [3 -(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] is preferred. Further, for example, hydrazine-based metal deactivators such as N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine and tris (2,4-di-t A phosphorus-based processing stabilizer such as -butylphenyl) phosphite may be used in combination.

  The amount of these compounds added is preferably 1 ppm to 1.0% by mass and more preferably 10 to 1,000 ppm by mass with respect to the cellulose derivative.

  In this Embodiment, the film thickness after drying of a cellulose-ester film has the preferable range of 20-150 micrometers as a finished film from a viewpoint of thickness reduction of a liquid crystal display device. Here, “after drying” refers to a film dried to a state where the amount of residual solvent in the film is 0.5% by mass or less.

  Here, when the film thickness of the cellulose ester film after winding is too thin, for example, the required strength as a protective film for a polarizing plate may not be obtained. If the film thickness is too thick, the advantage of thinning the film becomes less than the conventional cellulose ester film. To adjust the film thickness, control the dope concentration, pump feed volume, slit gap of the die of the casting die, extrusion pressure of the casting die, and the moving speed of the metal support to achieve the desired thickness. It is good to do. Further, as a means for making the film thickness uniform, it is preferable to use a film thickness detection means to feed back and adjust the programmed feedback information to each of the above devices.

  In the process from immediately after casting through the solution casting film forming method to drying, the atmosphere in the drying apparatus may be air, or may be performed in an inert gas atmosphere such as nitrogen gas or carbon dioxide gas. . However, of course, the danger of the explosion limit of the evaporating solvent in the dry atmosphere must always be considered.

  In the present embodiment, the cellulose ester film has a moisture content of preferably 0.1 to 5%, more preferably 0.3 to 4%, and even more preferably 0.5 to 2%.

  In the present embodiment, the cellulose ester film desirably has a transmittance of 90% or more, more preferably 92% or more, and further preferably 93% or more.

  In addition, the optical film manufactured by the method of the present embodiment has a haze of 0.3 to 2.0 when three sheets are stacked, and according to the optical film of the present embodiment, It has very low haze and has optical properties excellent in transparency and flatness.

  Here, the haze of the optical film may be measured using, for example, a haze meter (1001DP type, manufactured by Nippon Denshoku Industries Co., Ltd.) according to a method defined in JIS K 6714.

  Moreover, the tensile elasticity modulus of MD direction (conveyance direction) of the cellulose-ester film manufactured with the manufacturing method of the optical film by this Embodiment is 1500 MPa-3,500 MPa, and the tensile elasticity of TD direction (width direction). The rate is preferably 3,000 MPa to 4,500 MPa, and the ratio of the TD direction elastic modulus / MD direction elastic modulus of the film is preferably 1.40 to 1.90.

  Here, if the ratio of the elastic modulus in the TD direction / the elastic modulus in the MD direction of the optical film is less than 1.40, the sag of the central portion becomes large when winding a film having a width exceeding 1,650 mm, and the winding core Since sticking of a film increases, it is not preferable. Further, when the ratio of the elastic modulus in the TD direction / the elastic modulus in the MD direction exceeds 1.90, warpage occurs after heating on the deflecting plate, or the backlight is heated by the heat of the backlight when incorporated in the liquid crystal panel. Since the dimensional change behavior of the polarizing plate on the side and the surface side is greatly different, unevenness occurs at the corner, which is not preferable.

  As a specific method for measuring the tensile modulus of elasticity in the MD direction and TD direction of the film, for example, the method of JIS K 7217 can be mentioned.

  That is, using a tensile tester (TG-2KN, manufactured by Minebea Co., Ltd.), a sample was set at a chucking pressure: 0.25 MPa, a distance between marked lines: 100 ± 10 mm, and a pulling speed: 100 ± 10 mm / min. Pull on. As a result, from the obtained tensile stress-strain curve, the elastic modulus calculation start point is 10N, the end point is 30N, and the tangent line drawn between them is extrapolated to calculate the elastic modulus.

  The optical film produced by the method of the present embodiment is preferably used for a liquid crystal display member, specifically, a protective film for a polarizing plate. In particular, an optical film produced by the method of the present embodiment is preferably used in a protective film for a polarizing plate that has strict requirements for both moisture permeability and dimensional stability.

  By using the protective film for polarizing plates made of the optical film of the present embodiment, it is possible to provide a polarizing plate excellent in durability, dimensional stability, and optical isotropy as well as in a thin film.

  By the way, the polarizing film is a film that has been conventionally stretched by treating a film that can be stretched and oriented, such as a polyvinyl alcohol film, with a dichroic dye such as iodine. Since the polarizing film itself does not have sufficient strength and durability, a polarizing plate is generally obtained by adhering a cellulose ester film having no anisotropy as a protective film to both surfaces thereof.

  The polarizing plate may be prepared by laminating the optical film produced by the method of the present embodiment as a retardation film, or the optical film produced by the method of the present embodiment may be prepared as a retardation film. Alternatively, the protective film may be used as a direct attachment to the polarizing film. The method of bonding is not particularly limited, but can be performed with an adhesive composed of an aqueous solution of a water-soluble polymer. As this water-soluble polymer adhesive, a completely saponified polyvinyl alcohol aqueous solution is preferably used. Furthermore, a long polarizing plate is obtained by laminating a long polarizing film stretched in the longitudinal direction and treated with a dichroic dye and a long retardation film produced by the method of the present embodiment. Can do. A polarizing plate is a sticking type in which a peelable sheet is laminated on one or both sides thereof via a pressure-sensitive adhesive layer (for example, an acrylic pressure-sensitive adhesive layer). It can be easily attached to a cell or the like.

  The polarizing plate thus obtained can be used for various display devices. In particular, a liquid crystal display device using a VA mode liquid crystal molecule in which liquid crystal molecules are substantially vertically aligned when no voltage is applied, or a TN mode liquid crystal cell in which liquid crystal molecules are substantially horizontal and twisted when no voltage is applied. It is preferable to use for.

  By the way, a polarizing plate can be produced by a general method. For example, there is a method in which an optical film or a cellulose ester film is subjected to alkali saponification treatment, and a polyvinyl alcohol film is immersed and stretched in an iodine solution and bonded to both surfaces of a polarizing film using a completely saponified polyvinyl alcohol aqueous solution. is there. The alkali saponification treatment refers to a treatment of immersing the cellulose ester film in a high-temperature strong alkaline solution in order to improve the wetness of the water-based adhesive and improve the adhesiveness.

  The optical film produced by the method of this embodiment includes a hard coat layer, an antiglare layer, an antireflection layer, an antifouling layer, an antistatic layer, a conductive layer, an optical anisotropic layer, a liquid crystal layer, an alignment layer, and an adhesive layer. Various functional layers such as a layer, an adhesive layer, and an undercoat layer can be provided. These functional layers can be provided by a method such as coating or vapor deposition, sputtering, plasma CVD, or atmospheric pressure plasma treatment.

  Thus, the obtained polarizing plate is provided in the one or both surfaces of a liquid crystal cell, and a liquid crystal display device is obtained using this.

  In the present embodiment, the liquid crystal display device includes a liquid crystal cell in which rod-like liquid crystal molecules are sandwiched between a pair of glass substrates, a polarizing film disposed so as to sandwich the liquid crystal cell, and transparent protective layers disposed on both sides thereof. It has two polarizing plates.

  By using a protective film for a polarizing plate made of an optical film produced by the method of the present embodiment, it is possible to provide a polarizing plate excellent in durability, dimensional stability, and optical isotropy as well as in a thin film. it can. Furthermore, a liquid crystal display device using this polarizing plate or retardation film can maintain stable display performance over a long period of time.

  The optical film produced by the method of the present embodiment can also be used as a base material for an antireflection film or an optical compensation film.

  Hereinafter, the present embodiment will be described more specifically by way of examples, but the present invention is not limited to these examples.

Examples 1-4
(Preparation of dope)
The following materials were put into a closed container, heated, stirred and completely dissolved and filtered to prepare a dope. Silicon dioxide fine particles (Aerosil R972V) were added after being dispersed in ethanol.

(Dope composition)
Cellulose triacetate (acetyl substitution degree 2.88) 100 parts by weight Triphenyl phosphate 6 parts by weight Biphenyl diphenyl phosphate (liquid plasticizer) 6 parts by weight 5-chloro-2- (3,5-di-sec-butyl-2- Hydroxy phenyl-2H-benzotriazole (liquid UV absorber) 1 part by weight Methylene chloride 418 parts by weight Ethanol 23 parts by weight Aerosil R972V 0.1 part by weight (production of cellulose ester film)
The dope was filtered and a cellulose triacetate film was produced by the method of the present invention using the solution casting film forming apparatus shown in FIG.

  The dope after the filtration is adjusted to a temperature of 35 ° C., and is uniformly applied by a casting die (1) made of a coat hanger die on a metal support (2) made of an endless belt made of SUS316 at a temperature of 20 ° C. Casted with a film thickness. Here, the atmospheric temperature of the casting zone (A) was set to 30 ° C.

  In this embodiment, after the web (4) is peeled from the endless belt support (2), the web (4) between the casting zone (A) and the stretching zone (B) having different atmospheric temperatures is transferred. A high energy irradiation processing device composed of an ultraviolet irradiation device (5) is installed on both upper and lower sides in the inter-zone transition portion (21), and the web (4) that moves through the inter-zone transition portion (21) is subjected to ultraviolet irradiation treatment. gave.

  The atmospheric temperature in the stretching zone (B) is set to 45 ° C. Therefore, the temperature difference between the atmospheric temperature in the casting zone (A) and the atmospheric temperature in the stretching zone (B) is 15 ° C. It was.

As shown in FIG. 4, the ultraviolet irradiation device (5) is arranged on both upper and lower sides of the web (4), and as a high energy irradiation device, an excimer UV having an irradiance of 40 mJ / cm ² and an Xe ₂ wavelength of 172 nm. An excimer ultraviolet irradiation device (5) containing an (EUV) lamp was used.

  Here, the gap (d) from the surface of the quartz glass (q) of the excimer UV lamp to the web (4) is 1 mm in Example 1, 3 mm in Example 2, and 12 mm in Example 3. 4 was set to 20 mm.

  The web (4) is transported at a rate of 0.2 sec. Between the quartz glass panels of the excimer ultraviolet irradiation device (5), and the web (4) is transported during film formation. UV light was irradiated continuously. As a result, the additive volatile vapor flowing through the zone-to-zone transition portion (21) with the transition of the web (4) is decomposed into carbon dioxide, water, and the like to prevent the generation of condensation.

  Next, the web (4) is introduced into the tenter (B) in the stretching zone, and the web (4) is stretched in the width direction while being heated, and then the drying zone (C) at 130 ° C. is sufficient for the web. (4) was dried to finally obtain a cellulose ester film having a film thickness of 40 μm and a product width of 2300 mm.

  The stretching ratio in the width direction of the tenter in the stretching zone (B) was adjusted according to the width of the web (4) entering the stretching zone (B) so that a product width of 2300 mm could be obtained. That is, before the stretching zone (B), the web (4) having a large width shrinkage is stretched at a high stretching ratio, and the web (4) having a small width shrinkage is stretched at a lower stretching ratio. .

  Under these conditions, a cellulose triacetate film was formed continuously for 3 days, and the film formation of each example obtained was evaluated for the occurrence of condensation as described later.

Examples 5-8
According to the method of the present invention, a cellulose triacetate film is produced in the same manner as in Examples 1 to 4, but the difference from the case of Examples 1 to 4 is that the ambient temperature of the stretching zone (B) is 90 ° C. Therefore, the temperature difference between the atmospheric temperature of the casting zone (A) and the atmospheric temperature of the stretching zone (B) is 60 ° C.

  As a high energy irradiation apparatus, the excimer ultraviolet irradiation apparatus (5) of the type arrange | positioned at the upper and lower sides of the web (4) shown in FIG. 4 was used like the case of the said Examples 1-4.

  The gap (d) from the surface of the quartz glass (q) of the excimer UV lamp to the web (4) is 1 mm in Example 5, 3 mm in Example 6, 12 mm in Example 7, and Example 8 Then, it set to 20 mm and implemented.

Examples 9-12
According to the method of the present invention, a cellulose triacetate film is produced in the same manner as in Examples 1 to 4, except that the temperature of the stretching zone (B) is 145 ° C. Therefore, the temperature difference between the atmospheric temperature of the casting zone (A) and the atmospheric temperature of the stretching zone (B) is 115 ° C.

  As a high energy irradiation apparatus, the excimer ultraviolet irradiation apparatus (5) of the type arrange | positioned at the upper and lower sides of the web (4) shown in FIG. 4 was used like the case of the said Examples 1-4.

  The gap (d) from the surface of the quartz glass (q) of the excimer UV lamp to the web (4) is 1 mm in Example 9, 3 mm in Example 10, 12 mm in Example 11, and Example 12 Then, it set to 20 mm and implemented.

Examples 13-16
According to the method of the present invention, a cellulose triacetate film is produced in the same manner as in Examples 1 to 4, but the difference from the case of Examples 1 to 4 is that the web shown in FIG. It is the point which used the excimer ultraviolet irradiation device (5) of the type arrange | positioned only on the upper side of (4).

  The temperature difference between the atmospheric temperature in the casting zone (A) and the atmospheric temperature in the stretching zone (B) is 15 ° C.

  The gap (d) from the surface of the quartz glass (q) of the excimer UV lamp to the web (4) is 1 mm in Example 13, 3 mm in Example 14, 12 mm in Example 15, and Example 16 Then, it set to 20 mm and implemented.

Examples 17-20
According to the method of the present invention, a cellulose triacetate film is produced in the same manner as in Examples 13 to 16, except that the atmospheric temperature of the stretching zone (B) is 90 ° C. Therefore, the temperature difference between the atmospheric temperature of the casting zone (A) and the atmospheric temperature of the stretching zone (B) is 60 ° C.

  As the high energy irradiation device, an excimer ultraviolet irradiation device (5) of a type arranged only on the upper side of the web (4) shown in FIG. 5 was used as in Examples 13 to 16.

  The gap (d) from the surface of the quartz glass (q) of the excimer UV lamp to the web (4) is 1 mm in Example 17, 3 mm in Example 18, 12 mm in Example 19, and Example 20 Then, it set to 20 mm and implemented.

Examples 21-24
According to the method of the present invention, a cellulose triacetate film is produced in the same manner as in Examples 13 to 16, except that the ambient temperature in the stretching zone (B) is 145 ° C. Therefore, the temperature difference between the atmospheric temperature of the casting zone (A) and the atmospheric temperature of the stretching zone (B) is 115 ° C.

  As the high energy irradiation device, an excimer ultraviolet irradiation device (5) of a type arranged only on the upper side of the web (4) shown in FIG. 5 was used as in Examples 13 to 16.

  The gap (d) from the surface of the quartz glass (q) of the excimer UV lamp to the web (4) is 1 mm in Example 21, 3 mm in Example 22, 12 mm in Example 23, and Example 24. Then, it set to 20 mm and implemented.

Examples 25-28
Although the cellulose triacetate film is produced by the method of the present invention in the same manner as in Examples 1 to 4, the difference from the case of Examples 1 to 4 is that the direct energy shown in FIG. Alternatively, an atmospheric pressure plasma irradiation device (6) called a planar method is used. In addition, the atmospheric pressure plasma irradiation apparatus (6) is installed on the upper and lower sides of the web (4).

  The temperature difference between the atmospheric temperature in the casting zone (A) and the atmospheric temperature in the stretching zone (B) is 15 ° C.

  Here, the distance (d) between the plasma gas outlet of the atmospheric pressure plasma apparatus (6) and the web (4) is 1 mm in Example 25, 3 mm in Example 26, 12 mm in Example 27, In Example 28, it set and implemented to 20 mm, respectively.

The source gas of the atmospheric pressure plasma apparatus (6) was nitrogen only, and the amount of source gas used was 0.5 m ³ / min per 1 m of irradiation width. The atmospheric pressure at this time was 1.0 atmospheric pressure.

  While conveying the web (4) in the zone transition part (21) between the casting zone (A) and the stretching zone (B) having different atmospheric temperatures, an atmospheric pressure plasma irradiation treatment was performed.

  At this time, the web (4) was conveyed so that the plasma gas irradiation time to the web (4) was 0.1 sec, and plasma blowing gas was continuously irradiated during film formation.

  The plasma irradiation time referred to here is a certain point on the surface of the web (4) because it is difficult to measure the exact contact time between the radical contained in the plasma blowing gas and the web (4). However, the time required to move under the plasma blowing slit gap (h) by the gap was defined as the irradiation time. For example, when the blowing slit gap (h) is 2 mm and the moving speed of the web (4) is 2 mm / sec, the plasma irradiation time is 1 sec.

Examples 29-32
According to the method of the present invention, a cellulose triacetate film is produced in the same manner as in Examples 25 to 28. The difference from the cases of Examples 25 to 28 is that the atmospheric temperature in the stretching zone (B) is 90 ° C. Therefore, the temperature difference between the atmospheric temperature of the casting zone (A) and the atmospheric temperature of the stretching zone (B) is 60 ° C.

  As the high energy irradiation apparatus, the atmospheric pressure plasma irradiation apparatus (6) of the type arranged on both upper and lower sides of the web (4) shown in FIG. 6 was used as in Examples 25 to 28.

  The distance (d) between the gas gas outlet of the atmospheric pressure plasma apparatus (6) and the web (4) is 1 mm in Example 29, 3 mm in Example 30, and 18 mm in Example 31. In Example 32, it set to 30 mm and implemented.

Examples 33-36
According to the method of the present invention, a cellulose triacetate film is produced in the same manner as in Examples 25 to 28. The difference from the case of Examples 25 to 28 is that the atmospheric temperature in the stretching zone (B) is 145 ° C. Therefore, the temperature difference between the atmospheric temperature of the casting zone (A) and the atmospheric temperature of the stretching zone (B) is 115 ° C.

  As the high energy irradiation apparatus, the atmospheric pressure plasma irradiation apparatus (6) of the type arranged on both upper and lower sides of the web (4) shown in FIG. 6 was used as in Examples 25 to 28.

  The distance (d) between the plasma gas outlet of the atmospheric pressure plasma apparatus (6) and the web (4) is 1 mm in Example 33, 3 mm in Example 34, and 18 mm in Example 35. In Example 36, it set to 30 mm and implemented.

Examples 37-40
According to the method of the present invention, a cellulose triacetate film is produced in the same manner as in Examples 25 to 28. The difference from the cases of Examples 25 to 28 is that the remote or downflow method is called, FIG. The high-energy irradiation treatment apparatus comprising the atmospheric pressure plasma irradiation apparatus (6) shown in FIG. ) Only on the upper side, and the web (4) that moves between the zone transition portions (21) is subjected to atmospheric pressure plasma irradiation.

  The temperature difference between the atmospheric temperature in the casting zone (A) and the atmospheric temperature in the stretching zone (B) is 15 ° C.

  The distance (d) between the gas gas outlet of the atmospheric pressure plasma device (6) and the web (4) is 1 mm in Example 37, 3 mm in Example 38, and 18 mm in Example 39. In Example 40, it set and implemented to 30 mm, respectively.

The source gas for the plasma reaction was nitrogen only, and the amount used was 0.5 m ³ / min per 1 m of irradiation width. The atmospheric pressure at this time was 1.0 atmospheric pressure. While conveying the web (4) in the zone transition part (21) between the casting zone (A) and the stretching zone (B) having different atmospheric temperatures, the atmospheric pressure plasma irradiation treatment was performed.

  At this time, the web (4) was conveyed so that the irradiation time of the plasma gas to the web (4) was 0.002 sec, and plasma blowing gas was continuously irradiated during film formation.

  The plasma irradiation time referred to here is a certain point on the surface of the web (4) because it is difficult to measure the exact contact time between the radical contained in the plasma blowing gas and the web (4). However, the irradiation time was defined as the time required to move under the plasma blowing slit (h) by the gap. For example, when the gap between the blowing slits (h) is 2 mm and the moving speed of the web (4) is 2 mm / sec, the plasma irradiation time is 1 sec.

Examples 41-44
According to the method of the present invention, a cellulose triacetate film is produced in the same manner as in Examples 37 to 40. The difference from the case of Examples 37 to 40 is that the ambient temperature in the stretching zone (B) is 90 ° C. Therefore, the temperature difference between the casting zone (A) 0 ambient temperature and the stretching zone (B) ambient temperature is 60 ° C.

  As a high energy irradiation apparatus, as in the case of Examples 37 to 40, a normal pressure plasma irradiation apparatus (6) disposed only on the upper side of the web (4) shown in FIG. Atmospheric pressure plasma irradiation was performed to the web (4) which transfers the zone transition part (21) between A) and the extending | stretching zone (B).

  The distance (d) between the gas gas outlet of the atmospheric pressure plasma device (6) and the web (4) is 1 mm in Example 41, 3 mm in Example 42, and 18 mm in Example 43. In Example 44, 30 mm was set for each.

Examples 45-48
According to the method of the present invention, a cellulose triacetate film is produced in the same manner as in Examples 37 to 40. The difference from the case of Examples 37 to 40 is that the atmospheric temperature in the stretching zone (B) is 145 ° C. Therefore, the temperature difference between the atmospheric temperature of the casting zone (A) and the atmospheric temperature of the stretching zone (B) is 115 ° C.

  As a high energy irradiation apparatus, as in the case of Examples 37 to 40, a normal pressure plasma irradiation apparatus (6) disposed only on the upper side of the web (4) shown in FIG. Atmospheric pressure plasma irradiation was performed to the web (4) which transfers the zone transition part (21) between A) and the extending | stretching zone (B).

  The distance (d) between the plasma gas outlet of the atmospheric pressure plasma apparatus (6) and the web (4) is 1 mm in Example 45, 3 mm in Example 46, and 18 mm in Example 47. In Example 48, 30 mm was set for each.

Comparative Examples 1-3
The cellulose triacetate film is formed using the same material as in Examples 1 to 4 above. However, in the solution casting film forming apparatus, when the web is sequentially passed through zones having different atmospheric temperatures, casting is performed. An ultraviolet irradiation device is provided between any one of the zone-to-zone transitions between the zone and the stretching zone, between the stretching zone and the drying zone, or between all the zone-to-zone transitions. And / or without an atmospheric pressure plasma apparatus.

  The temperature difference between the atmospheric temperature of the casting zone (A) and the atmospheric temperature of the stretching zone (B) is 15 ° C. in Comparative Example 1, 70 ° C. in Comparative Example 2, 115 ° C. in Comparative Example 3, Each was set and implemented.

Comparative Examples 4-6
The cellulose triacetate film is formed using the same material as in Examples 1 to 4 above, but as shown in FIG. 8, in the conventional solution casting film forming apparatus, the casting zone (A) and At the transition zone between zones where the web (14) between the stretching zone (B) passes, the atmospheric temperature of the casting zone (A) and the atmospheric temperature of the stretching zone (B) at the inlet and outlet of the transition zone between zones. An air curtain for blowing wind (air) (13) having an intermediate temperature was installed to form a film. The air blowing speed of air (13) from the air curtain was 5 m / sec.

  The temperature difference between the atmospheric temperature of the casting zone (A) and the atmospheric temperature of the stretching zone (B) is 15 ° C. in Comparative Example 4, 70 ° C. in Comparative Example 5, 115 ° C. in Comparative Example 6, Each was set and implemented.

  Next, using the cellulose triacetate films prepared in Examples 1 to 48 and Comparative Examples 1 to 6 as a protective film for a polarizing plate, various polarizing plates were prepared by the following methods and evaluated.

(Preparation of polarizing film)
A long polyvinyl alcohol film having a thickness of 120 μm was uniaxially stretched (temperature: 110 ° C., stretch ratio: 5 times). This was immersed in an aqueous solution composed of 0.075 g of iodine, 5 g of potassium iodide, and 100 g of water for 60 seconds, and then immersed in an aqueous solution at 68 ° C. composed of 6 g of potassium iodide, 7.5 g of boric acid, and 100 g of water. . This was washed with water and dried to obtain a long polarizing film.

(Preparation of polarizing plate)
Subsequently, according to the following processes 1-5, the polarizing film and the cellulose triacetate film optical film produced in Examples 1-48 and Comparative Examples 1-6 were bonded together, and the polarizing plate was produced.

  Step 1: The cellulose triacetate films prepared in Examples 1-48 and Comparative Examples 1-6 were immersed in a 2 mol / L sodium hydroxide solution at a temperature of 50 ° C. for 90 seconds, and then Washed with water and dried.

  On the other hand, a commercially available long cellulose ester film was immersed in a 2 mol / L sodium hydroxide solution at a temperature of 50 ° C. for 90 seconds, then washed with water and dried.

  Process 2: Said long polarizing film was immersed in the polyvinyl alcohol adhesive tank of 2 mass% of solid content for 1-2 seconds.

  Step 3: Excess adhesive adhered to the polarizing film in Step 2 was lightly removed, and the long cellulose triacetate films of Examples 1 to 48 and Comparative Examples 1 to 6 were subjected to alkali treatment in Step 1 and a commercially available length The sample was sandwiched between and placed in a scale with a cellulose ester film.

Process 4: These films were laminated together at a speed of about 2 m / min at a pressure of ^{20 to} 30 N / cm ² with two rotating rollers. At this time, care was taken to prevent bubbles from entering.

  Step 5: The film sample produced in Step 4 was dried for 2 minutes in a dryer at 80 ° C. to produce a polarizing plate.

(Production of liquid crystal display panel)
Carefully peel off the polarizing plate on the outermost surface of a commercially available liquid crystal display panel (NEC color liquid crystal display, MultiSync, LCD1525J, model name LA-1529HM), and paste the various polarizing plates prepared above in accordance with the polarization direction. A liquid crystal display panel was produced.

  In order to evaluate the cellulose triacetate films prepared in Examples 1 to 48 and Comparative Examples 1 to 6, evaluation was performed by the method shown below.

  The cellulose triacetate films obtained in Examples 1 to 48 and Comparative Examples 1 to 9 were evaluated for visual observation of condensed dirt, pure water contact angle, variation width of crossed Nicol transmittance, and these films as protective films. The color unevenness of the polarizing plate used as a visual observation was observed. The obtained results are shown in Table 1 below.

(Condensation dirt evaluation)
The cellulose triacetate film produced in Examples 1-36 and Comparative Examples 1-9 is spread on a flat evaluation table with a black rubber cloth, and the green lamp is irradiated obliquely, so that the condensation adheres to the film surface. Then, the stain pattern that looks whitish was visually observed.

◎: There is no pattern of condensed dirt. ○: There is a part that looks like a pattern of condensed dirt.
Level that does not affect the product at all △: Condensed dirt pattern and minute deformation can be confirmed in the part ×: Condensed dirt pattern that can be seen at a glance and many deformations of the part can be seen at a glance, cannot be used as a product Level (Measurement of pure water contact angle)
When the surface of each cellulose triacetate film prepared in Examples 1 to 36 and Comparative Examples 1 to 9 was dropped 3 mm ^{3 of} pure water using a contact angle meter PG-X manufactured by Matsubo Co., Ltd. The target contact angle was measured.

Here, at an interval of 50 mm in the width direction and longitudinal direction of the film, an area of 1 m ² on the film was measured at five points at each position and its vicinity, and an average value of static contact angles was obtained. The average value of the data and the width of the upper limit value and the lower limit value of the static contact angle were evaluated as the variation width of the contact angle.

  Here, as a guide, if the variation width of the contact angle is 10 ° or less, the surface physical properties of the film are uniform, and even in post-processing such as coating, there is no repellency of the coating liquid, and a uniform treatment can be expected. Further, when the variation width of the contact angle exceeds 10 °, failure such as repellency or unevenness of the coating liquid is likely to occur during post-processing such as application.

[Measurement of Cross Nicol Transmittance (CNT)]
Using a polarizing film measuring device (VAP-7070) manufactured by JASCO Corporation, at a measurement wavelength of 600 nm, the crossed Nicols transmittance (CNT) at intervals of 50 mm in the width direction of the film and at intervals of 50 mm in the lengthwise direction of 300 mm The difference between the average value of all data and the most dissimilar value was defined as the variation width (× 10 ⁻⁵ %) of the crossed Nicols transmittance (CNT) here.

  The variation width of the crossed Nicols transmittance (CNT) serves as an index of the retardation value of the film. The smaller the variation width, the lower the retardation value of the film.

(Width shrinkage)
Transition between zones from different zone temperatures, for example, the web width (W1) on the final roll on the web exit side of the upstream zone and the web width (W2) on the roll at the web entrance of the next zone. The width shrinkage rate (%) at the part was determined by the following formula.

Width shrinkage rate (%) = {(W1−W2) / W1} × 100
(Visual evaluation of polarizing plate)
About each liquid crystal display panel produced as mentioned above, the color unevenness which looks whitish when it sees from the front and diagonally by several evaluators was observed, and it was set as evaluation of a polarizing plate.

○: None of the evaluators can see the color unevenness at all. △: The evaluator may slightly see the color unevenness.
Level that can be used as a product ×: Level at which many evaluators can confirm color unevenness and cannot be used as a product. Table 1 below shows casting zones (A) in Examples 1 to 48 and Comparative Examples 1 to 6 The temperature difference between the ambient temperature of the stretching zone (B) and the ambient temperature of the stretching zone (B) is shown together, and the type of the high-energy irradiation processing apparatus used in Examples 1-48 and the processing apparatus used in Comparative Examples 4-6 And the gap (d) between the processing device and the web (4) are also shown.

  As is clear from the results in Table 1 above, as shown in Examples 1 to 38 of the present invention, when the web (4) is sequentially passed through zones having different ambient temperatures, the casting cooling and solidifying zone (A) and A high energy irradiation treatment device comprising an excimer ultraviolet irradiation device (5) or a normal pressure plasma irradiation device (6) is installed in the zone transition portion (21) where the web (4) between the stretching zone (B) moves. Then, by applying high energy irradiation treatment to the web (4) that migrates between the zone-to-zone transition part (21), in the film formation for 3 days, the occurrence of condensation stains such as additives on the film surface is not seen, Moreover, both the variation width of the contact angle and the variation width of the crossed Nicol transmittance (CNT) were small, and even after being processed into a polarizing plate, color unevenness that looked whitish was not confirmed. From this result, a predicted result was obtained that the film forming operation could be carried out without problems in film quality even with continuous film forming for about one month.

  On the other hand, in Comparative Examples 1 and 2, whitish dirt and color unevenness were observed on the film surface from the start of film formation to a level where it could not be used as a product in just 3 days. There was no choice but to work, and productivity was quite low. Condensation contamination of the transport roll reduces the gripping force of the web on the roll, and the width shrinkage force due to the drying and transport tension of the web wins, causing the width shrinkage, and the web width before the tenter Since it became narrow, in order to obtain a product width of 2300 mm, the tenter stretching ratio had to be increased, and as a result, the haze of the web increased and the width of CNT variation related to it increased.

  As described above, according to the present invention, in the method for producing an optical film by the solution casting film forming method, by installing the atmospheric pressure plasma device and / or the ultraviolet irradiation device at the zone-to-zone transition part having a different atmospheric temperature, By decomposing the volatile gas of the additive, condensed dirt can be eliminated, and an optical film having optical properties excellent in transparency and flatness can be produced with high productivity. Thereby, it can respond to the request | requirement of thickness reduction, widening, and quality improvement, such as a protective film for polarizing plates.

  In addition, the manufacturing method of the optical film according to the present invention, the optical film, the polarizing plate, and the detailed configuration of each configuration constituting the display device and the detailed operation are appropriately changed without departing from the gist of the present invention. Is possible.

It is a flow sheet which shows 1st Embodiment of the apparatus which enforces the manufacturing method of the optical film by the solution casting film forming method in this invention. It is a flow sheet which shows 2nd Embodiment of the apparatus which enforces the manufacturing method of the optical film by the solution casting film forming method in this invention. It is a flow sheet which shows 3rd Embodiment of the apparatus which enforces the manufacturing method of the optical film by the solution casting film forming method in this invention. It is explanatory drawing for demonstrating the principle of the excimer ultraviolet irradiation device used in the manufacturing method of the optical film of this Embodiment. It is explanatory drawing for demonstrating the principle of another excimer ultraviolet irradiation device used in the manufacturing method of the optical film of this Embodiment. It is explanatory drawing for demonstrating the principle of the atmospheric pressure plasma apparatus used in the manufacturing method of the optical film of this Embodiment. It is explanatory drawing for demonstrating the principle of the one normal pressure plasma apparatus used in the manufacturing method of the optical film of this Embodiment. It is explanatory drawing for demonstrating the air curtain used in the manufacturing method of the conventional optical film.

Explanation of symbols

1: Casting die 2: Stainless steel rotation drive endless belt (metal support)
3: Stripping roll 4: Web 5: Excimer ultraviolet irradiation device 6: Atmospheric pressure plasma device 7: Air blowing for web drying 8: Winding device 9: Winding drum 10: Rotating drive drum 21: Inter-zone transition section 22: Transition zone A: Casting zone B: Stretching zone C: Drying zone a: Electrode b: Electrode g: Raw material gas d: Distance between surface treatment apparatus and web h: Plasma gas blowing slit gap p: Purge gas r: Reflection Plate u: Excimer UV lamp q: Quartz glass

Claims (6)

  A flow in which a resin solution (dope) containing a thermoplastic resin, an organic solvent, and an additive is cast from a casting die onto a metal support to form a cast film (web) and to peel the web from the support. It comprises a stretching zone (A), a stretching zone (B) for stretching the web with a tenter, and a drying zone (C) for drying the web. After the casting zone (A), the stretching zone (B) and the drying zone In the method for producing an optical film by the solution casting film forming method in which any one of (C) is arranged and then the other is arranged, the web is divided into zones between zones having different atmospheric temperatures. When sequentially passing through the inter-zone transition section, an ultraviolet irradiation device and / or an atmospheric pressure plasma apparatus is installed at any one of the inter-zone transition sections or all inter-zone transition sections among the inter-zone transition sections where the web moves. do it, The web to migrate transition between over emissions, characterized by ultraviolet radiation and / or plasma irradiation, method for producing an optical film.   The method for producing an optical film according to claim 1, wherein the difference in the atmospheric temperature between zones having different atmospheric temperatures is in the range of 10 ° C. or higher and 120 ° C. or lower.   The method for producing an optical film according to claim 1, wherein the thermoplastic resin is a cellulose ester resin.   It manufactured with the manufacturing method of the optical film as described in any one of Claims 1-3, The optical film characterized by the above-mentioned.   A polarizing plate comprising the optical film according to claim 4 on at least one surface.   A display device comprising the polarizing plate according to claim 5.

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